Dart tests configured to be executed in random order.

* throw error on primary key set

* relax final on collections

fix tests

* fix setters in generated constructor to use RealmObject.set directly

* fix generator tests

* run realm_dart tests on generator change.

test only on Linux

* fix working directory

* fix workflow

* fix coverage file path

* get submodule

* clarify readme

* fix link

* handle PR feedback

* fix code samples

* run CI on every change

* use stable channel on CI

…eys and properties (#248)

Samples updated not to require final for properties, primary keys and lists when generating models.

* Realm object isValid and realm list isValid implementation
* Tests added for property isValid of RealmList and RealmObject

# Conflicts:
#	.github/workflows/realm-dart-linux.yml
#	test/realm_test.dart